In general, in a suspension system, a suspension spring is provided together with a shock absorber in order to absorb various types of vibration or impact, which is transmitted from a road surface when a vehicle travels, and to improve ride quality. The suspension spring of the suspension system may be classified into a leaf spring, a coil suspension spring, an air suspension system, and the like, and the air suspension system is advantageous in that a height of the vehicle may be constantly maintained or adjusted, but because a device for adjusting an amount of air according to a load, a device for compressing air, and the like are additionally required, the air suspension system is restrictively and mainly used for a large-scale vehicle such as a bus, or a high-grade passenger vehicle.
In particular, the high-grade vehicle uses a system for adjusting a height of a vehicle body for the purpose of ride quality, driving stability, and improvement in fuel efficiency. As representative methods, there are an air suspension system in which an air suspension spring is mounted instead of the existing coil suspension spring so as to adjust a height of the vehicle body by air flowing into and out of the air suspension spring, and an active body control (ABC) system of Benz which adjusts a height of a surface, on which the coil suspension spring is mounted, using hydraulic pressure.
As a technology in the related art relevant to the air suspension system, Korean Patent Application Laid-Open No. 10-2010-0127395 (Dec. 6, 2010) discloses “Hybrid Air Suspension System for Easily Adjusting Height of Vehicle”.
The hybrid air suspension system for easily adjusting a height of a vehicle is characterized in that the hybrid air suspension system connects a vehicle body and a wheel, and uses inflow and outflow of air so as to absorb a shock of the vehicle body and adjust a height of a vehicle.
The ABC system requires very high costs and has a complicated system configuration because a dedicated hydraulic actuator, piping for hydraulic pressure, and the like need to be considered.
The air suspension system may be more environmentally friendly than using hydraulic pressure and may be configured with a relatively simple structure because the air suspension system uses air, but pneumatic lines need to be connected at each corner in order to control pneumatic pressure, and an air compressor is indispensably required in order to control a solenoid pneumatic valve of a separate air suspension spring and produce high-pressure air.
Accordingly, because costs of the air suspension system are also higher than other systems in the vehicle, the air suspension system has been mainly used merely in a high-grade vehicle up to now.